It is known to produce a dialysis fluid on-line from fresh water and one or more concentrates. The fresh water generally contains no microorganisms and the concentrates are normally sterile, but it is nevertheless difficult to guarantee that the dialysis fluid produced on-line always meets the very stringent sterility requirements imposed in extracorporeal blood treatments.
In hemodiafiltration, it is known to produce a substitution fluid on-line from a dialysis fluid. The substitution fluid in particular should satisfy the stringent requirements concerning sterility.
In order to enable the sterility of the dialysis fluid and substitution fluid, known blood treatment apparati contain sterile filters, which can be replaced after one use or after they have been used several times. European Patent No. EP 0 930 080 A1 describes a blood treatment apparati which has a first sterile filter for producing a sterile dialysis fluid from fresh water and from a dialysis fluid concentrate, and a second sterile filter for producing a sterile substitution fluid from the dialysis fluid. Both sterile filters are arranged in the dialysis fluid circuit upstream of the dialyzer and are flushed with the dialysis fluid.
In practice it is desirable that a sterile filter provided for a blood treatment apparatus is actually fitted in the apparatus. Otherwise there is a risk that the dialysis fluid and/or substitution fluid may not be sterile. Automatic detection of whether the apparatus is fitted with a filter typically requires additional equipment and costs.